Method for color saturation adjustment in an RGB color system

ABSTRACT

The present invention relates to a method for adjusting the saturation levels of the pixels of a time varying image being represented by RGB color sample vectors {right arrow over (C)} in an RGB color system. The method does not require the RGB color sample vectors {right arrow over (C)} to be converted into YUV samples in order to subsequently perform saturation adjustment. The method includes steps of: decomposing an RGB color sample vector {right arrow over (C)} into a white vector {right arrow over (w)} and a color tone vector {right arrow over (C)} T ; obtaining a saturation adjusted color tone vector {right arrow over (C T   o )} by multiplying the color tone vector {right arrow over (C)} T  by a saturation adjustment parameter; obtaining a saturation adjusted RGB color sample vector {right arrow over (C)} o  by adding the white vector {right arrow over (w)} and the saturation adjusted color tone vector {right arrow over (C T   o )}; and using the saturation adjusted RGB color sample vector {right arrow over (C)} o  to represent a color pixel of an output image.

This application is a Divisional Patent Application of U.S. patentapplication Ser. No. 10/230,827, filed Aug. 29, 2002.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method for adjusting the saturationlevels of the pixels of a time varying image being represented using RGBsignals in an RGB color system. The method does not require the RGBsignals to be converted into YUV signals in order to subsequentlyperform saturation adjustment. Hence, the associated H/W complexityrequired to perform the inventive method is low when compared to thatrequired to perform the typical saturation level adjusting method.

The luminance and chromatic component Y, U, V color system, also knownas the luminance and color difference color system (Y, R−Y,B−Y) is thecolor system that is most widely used in video systems. For example, ina digital TV system, the Y, U, and V signals of a video are compressedand transmitted. In such a system, since the color information isembedded in the chroma signals U and V, the color saturation level issimply adjusted by multiplying the chroma signals U and V by a colorsaturation adjusting gain a as expressed by the following equations:U _(o) =α·U and V _(o) =α·V.U_(o) and V_(o) now represent color adjusted chroma signals. FIG. 1 is ablock diagram of a prior art color saturation adjusting circuit 10 thatcan be used to multiply the sample values of the chroma signals U and Vby the color saturation adjusting gain α. Note that if the colorsaturation adjusting gain α=0, the resulting sample value will have nocolor. If the color saturation adjusting gain α>1, then the color of theresulting sample value will be enriched.

In a prior art RGB color system, color saturation adjustment isperformed using the color saturation adjustment circuit 12 shown in FIG.2. Each RGB input sample vector is converted to a YUV sample value, andthe color saturation adjusting method shown in FIG. 1 is performed oneach YUV sample value. The output color saturation adjusted RGB samplevectors are then obtained by converting the Y₀, U₀, V color samplevalues to RGB color sample vectors. As can be seen, considerablecomputation is required for the conversions.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method forcolor saturation adjustment in an RGB color system which does notrequire the RGB color sample vectors to be converted into luminance andchroma samples in order to adjust the saturation levels of the RGB colorsample vectors.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a method for adjusting a color saturationlevel of at least one color pixel of an input image obtained from a timevarying RGB video signal. The method includes steps of: obtaining an RGBcolor sample vector {right arrow over (C)} representing the color pixelof the input image obtained from the time varying RGB video signal;decomposing the RGB color sample vector {right arrow over (C)} into awhite vector {right arrow over (w)} and a color tone vector {right arrowover (C)}_(T); obtaining a saturation adjusted color tone vector {rightarrow over (C_(T) ^(o))} by multiplying the color tone vector {rightarrow over (C)}_(T) by a saturation adjustment parameter; obtaining asaturation adjusted RGB color sample vector {right arrow over (C)}_(o)by adding the white vector {right arrow over (w)} and the saturationadjusted color tone vector {right arrow over (C_(T) ^(o))}; and usingthe saturation adjusted RGB color sample vector {right arrow over(C)}_(o) to represent a color pixel of an output image.

In accordance with an added feature of the invention, the saturationadjustment parameter is constructed such that the saturation level ofthe saturation adjusted color tone vector {right arrow over (C_(T)^(o))} will not exceed a predetermined limit value.

In accordance with an additional feature of the invention, thesaturation adjustment parameter is constructed as a color saturationadjusting gain α, and it is ensured that when the color saturationadjusting gain α equals zero, the saturation adjusted RGB color samplevector {right arrow over (C)}_(o) becomes a gray value. This isaccomplished by performing the following additional steps: a luminancevector {right arrow over (Y)} is defined where each component of theluminance vector {right arrow over (Y)} is a luminance value obtainedfrom the RGB color sample vector {right arrow over (C)}; the saturationadjustment parameter is configured to include at least a colorsaturation adjusting gain α; a gray mixing ratio α_(g) is obtained byselecting a minimum value from the group consisting of one and the colorsaturation adjusting gain α; and a gray level adjusted vector isobtained by multiplying the luminance vector {right arrow over (Y)} by aquantity obtained by subtracting the gray mixing ratio α_(g) from one.In addition, the step of obtaining the saturation adjusted RGB colorsample vector {right arrow over (C)}_(o) is performed by: before addingthe white vector {right arrow over (w)} and the saturation adjustedcolor tone vector {right arrow over (C_(T) ^(o))}, multiplying the whitevector {right arrow over (w)} by the gray mixing ratio α_(g); and whenadding the white vector {right arrow over (w)}, which has beenmultiplied by the gray mixing ratio α_(g), and the saturation adjustedcolor tone vector {right arrow over (C_(T) ^(o))}, also adding thereto,the gray level adjusted vector to obtain the saturation adjusted RGBcolor sample vector {right arrow over (C)}_(o). The color saturationadjusting gain a can be manually obtained from an adjustment by a userof the color system, or can be automatically set by an appropriatecircuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a prior art color saturation adjustingcircuit;

FIG. 2 is a block diagram of a prior art color saturation adjustingcircuit that is used in an RGB color system;

FIG. 3 shows a graphical representation of the decomposition of an RGBcolor sample vector into a white vector and a color tone vector;

FIG. 4 is a block diagram of a circuit for performing an example of afirst embodiment of the method for color saturation adjustment;

FIG. 5 is a block diagram of a circuit for performing another example ofthe first embodiment of the method for color saturation adjustment;

FIG. 6 is a block diagram of a circuit for performing an example of asecond embodiment of the method for color saturation adjustment;

FIG. 7 is a block diagram of a circuit for performing another example ofthe second embodiment of the method for color saturation adjustment;

FIG. 8 is a block diagram of two multipliers;

FIG. 9 is a block diagram of a circuit for performing a first embodimentof a method of calculating a saturation adjusted color tone vector{right arrow over (C_(T) ^(o))};

FIG. 10 is a block diagram of a circuit for performing a secondembodiment of the method of calculating the saturation adjusted colortone vector {right arrow over (C_(T) ^(o))};

FIGS. 11-13 are graphs of mathematical functions;

FIG. 14 is a block diagram of a circuit for performing a thirdembodiment of the method of calculating the saturation adjusted colortone vector {right arrow over (C_(T) ^(o))}; and

FIG. 15 is a flowchart showing the steps performed in a fourthembodiment of the method of calculating the saturation adjusted colortone vector {right arrow over (C_(T) ^(o))}.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following text uses a single digital RGB color sample vector {rightarrow over (C)}=(R,G,B) to explain the invention. It should be readilyapparent, however, that in a practical application, the inventive methodwill be applied to a plurality of digital RGB color sample vectors{right arrow over (C)} representing the images obtained from the timevarying RGB video signals of an RGB color system.

The invention begins with decomposing a given digital RGB color inputsample vector {right arrow over (C)}=(R,G,B) into two componentsaccording to the following equation:{right arrow over (C)}={right arrow over (w)}+{right arrow over (C)}_(T).  (1)Here, {right arrow over (w)} represents a white vector and {right arrowover (C)}_(T)=(R_(T),G_(T),B_(T)) represents a color tone vectorassociated with the color input sample vector. The white vector {rightarrow over (w)} presumably contains the lightness quantity and the colortone vector {right arrow over (C)}_(T)=(R_(T),G_(T),B_(T)) contains thecolor information. FIG. 3 shows a graphical representation of thisdecomposition. The range of the color samples is assumed to be0≦R,G,B≦255, however, the invention can be used with color sampleshaving any range. Note that the direction of the color tone vector{right arrow over (C)}_(T) is associated with the “hue”, while themagnitude of the color tone vector {right arrow over (C)}_(T) isassociated with the “saturation”.

A first embodiment of the method for color saturation adjustment isbased on applying the following equation:{right arrow over (C)} _(o) ={right arrow over (w)}+P·{right arrow over(C)} _(T) ={right arrow over (w)}+{right arrow over (C _(T)^(o))}.  (2a)Here, P is a saturation adjustment parameter, which when multipliedagainst the color tone vector {right arrow over (C)}_(T), works toadjust the saturation of the color tone vector {right arrow over(C)}_(T). The vector P·{right arrow over (C)}_(T) represents asaturation adjusted color tone vector {right arrow over (C_(T) ^(o))}.The vector {right arrow over (C)}_(o) is a saturation adjusted RGB colorsample vector, which can be output to represent a pixel of an outputimage.

Subsequently, in this text, four specific examples of methods areprovided that can be used to obtain the saturation adjusted color tonevector {right arrow over (C_(T) ^(o))}. These methods differ in thespecific form of the saturation adjustment parameter P that is used. Thesaturation adjustment parameter P can take the form of a colorsaturation adjusting gain α. This color saturation adjusting gain a canbe obtained from the actions of a user of the system or from a circuitconstructed to set the color saturation adjusting gain α. The saturationadjustment parameter P can alternatively include two factors, namely acolor saturation adjusting gain a and a saturation limiting parameter β,which are multiplied together. In an additional alternative, thesaturation adjustment parameter P can be a variable denoted by r. Thesaturation adjustment parameter P can also take the form of a real coloradjusting gain x. The specific forms of the saturation adjustmentparameter P will become clear with regard to further explanationsprovided later on in this text.

An example of the first embodiment of the method for color saturationadjustment will be further explained in a version in which thesaturation adjustment parameter P takes the form of a color saturationadjusting gain α, where (α≧0). This example of the first embodiment ofthe method for color saturation adjustment will then be based onapplying the following equation:{right arrow over (C)} _(o) ={right arrow over (w)}+α·{right arrow over(C)} _(T) ={right arrow over (w)}+{right arrow over (C _(T)^(o))}.  (2b)In equation (2b), it can be seen that the saturation adjusted color tonevector {right arrow over (C_(T) ^(o))} equals α·{right arrow over(C)}_(T). Note that {right arrow over (C)}_(o)={right arrow over (w)} ifα=0 (no color), {right arrow over (C)}_(o)={right arrow over (C)} whenα=1, and the color saturation level is increased if α>1.

FIG. 4 shows a block diagram of a circuit 20 for performing the exampleof the first embodiment of the method for color saturation adjustment inwhich the saturation adjustment parameter P takes the form of a colorsaturation adjusting gain α. The white and color tone separator 22decomposes the input color vector {right arrow over (C)}=(R,G,B) into awhite vector {right arrow over (w)} and a color tone vector {right arrowover (C)}_(T)=(R_(T),G_(T),B_(T)) as described by equation (1). Thesaturation adjusted color tone vector {right arrow over (C)}_(T) ^(o) isobtained using the multiplier 24, which performs the operation {rightarrow over (C)}_(T) ^(o)=α·{right arrow over (C)}_(T). The saturationadjusted RGB color sample vector {right arrow over (C)}_(o) is obtainedfrom the vector summer 26, which adds the white vector {right arrow over(w)} and the saturation adjusted color tone vector {right arrow over(C_(T) ^(o))}.

The input color vector {right arrow over (C)}=(R,G,B) can be decomposedinto a white vector {right arrow over (w)} and a color tone vector{right arrow over (C)}_(T)=(R_(T),G_(T),B_(T)) using any of a number ofdifferent decompositions. Although, the invention is not meant to belimited to any specific decomposition, the decomposition can beperformed, for example, by using any of the following decompositions:{right arrow over (C)} _(T)=(R−Y,G−Y,B−Y) and {right arrow over(w)}=(Y,Y,Y), where Y is a luminance value;  (3)

$\begin{matrix}{{{\overset{\rightarrow}{C}}_{T} = {{\left( {{R - X},{G - X},{B - X}} \right)\mspace{11mu}{and}\mspace{14mu}\overset{\rightarrow}{w}} = \left( {X,X,X} \right)}},{{{{where}\mspace{14mu} X} = \frac{R + G + B}{3}};{and}}} & (4) \\{{{\overset{\rightarrow}{C}}_{T} = {\left( {{R - \frac{G + B}{2}},{G - \frac{R + B}{2}},{B - \frac{R + G}{2}}} \right)\mspace{11mu}{and}}}\;{\overset{\rightarrow}{w} = {\left( {\frac{G + B}{2},\frac{R + B}{2},\frac{R + G}{2}} \right).}}} & (5)\end{matrix}$FIG. 5 shows a block diagram of a circuit 30 for performing the firstembodiment of the method in which the decomposition described inequation (3) is performed. The white vector calculation circuit 32calculates a luminance value Y from the RGB color sample vector {rightarrow over (C)} and constructs a white vector {right arrow over (w)}.Each component of the white vector {right arrow over (w)} is equal tothe luminance value Y. The vector summer 34 subtracts the white vector{right arrow over (w)} from the RGB color sample vector {right arrowover (C)} to obtain the color tone vector {right arrow over (C_(T))}.The multiplier 36 multiplies the color tone vector {right arrow over(C_(T))} by the color saturation adjusting gain a to obtain thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))}.The vector summer 38 adds the saturation adjusted color tone vector{right arrow over (C_(T) ^(o))} and the white vector {right arrow over(w)} to obtain the saturation adjusted RGB color sample vector {rightarrow over (C)}_(o). It is assumed that the color saturation adjustinggain α is equal to or greater than zero.

Turning our attention to the case when the color saturation adjustinggain α=0 in equation (2b), note that the saturation adjusted RGB colorsample vector {right arrow over (C)}_(o) may not be a gray valuedepending on the choice of the color tone vector {right arrow over(C_(T))} or equivalently on the choice of the white vector {right arrowover (w)}. For instance, if we choose to use equation (3) for thedecomposition, the saturation adjusted RGB color sample vector {rightarrow over (C)}_(o) will be (Y,Y,Y) when the color saturation adjustinggain α=0. This implies that the saturation adjusted RGB color samplevector {right arrow over (C)}_(o) is a gray value. However, if we chooseto use equation (4) for the decomposition, the saturation adjusted RGBcolor sample vector {right arrow over (C)}_(o) will be (X,X,X) when α=0.In this case, the saturation adjusted RGB color sample vector {rightarrow over (C)}_(o) becomes a gray value, but it is somewhat differentfrom the typical gray value denoted as Y. Furthermore, if we choose touse equation (4) for the decomposition, the saturation adjusted RGBcolor sample vector {right arrow over (C)}_(o) will be

$\left( {\frac{G + B}{2},\frac{R + B}{2},\frac{R + G}{2}} \right)$when α=0, which is not a gray value, in general. In most cases, it isdesirable to ensure that the saturation adjusted RGB color sample vector{right arrow over (C)}_(o) becomes a gray value whose gradation level isassociated with the luminance value of the input signal {right arrowover (C)}=(R,G,B) when α=0. For this purpose, a gray mixing ratio isdefined as:α_(g)=min(1.0,α).

A second embodiment of the method for color saturation adjustment isbased on applying the following equation:{right arrow over (C)} _(o) ={right arrow over (Y)}·(1−α_(g))+{rightarrow over (w)}·α _(g) +P·{right arrow over (C)} _(T); or{right arrow over (C)}_(o)={right arrow over (Y)}·(1−α_(g))+{right arrowover (w)}·α_(g)+{right arrow over (C _(T) ^(o))}; where {right arrowover (Y)}=(Y,Y,Y).  (6a)As with the first embodiment, P is the saturation adjustment parameterand {right arrow over (C_(T) ^(o))} is a saturation adjusted color tonevector. It should be clear that the second embodiment of the method forcolor saturation adjustment is equivalent to the first embodiment exceptfor the fact that additional steps are performed. In particular, thegray mixing ratio α_(g) is multiplied with the white vector {right arrowover (w)} before the summation is performed, and the term {right arrowover (Y)}·(1−α_(g)) is included in the summation. The term {right arrowover (Y)}·(1−α_(g)) is defined as a gray level adjusted vector.

An example of the second embodiment of the method for color saturationadjustment will be further explained in a version in which thesaturation adjustment parameter P takes the form of a color saturationadjusting gain α, where (α≧0). This example of the second embodiment ofthe method for color saturation adjustment will then be based onapplying the following equation:{right arrow over (C)} _(o) ={right arrow over (Y)}·(1−α_(g))+{rightarrow over (w)}·α _(g) +α·{right arrow over (C)} _(T); where {rightarrow over (Y)}=(Y,Y,Y).  (6b)The saturation adjusted RGB color sample vector {right arrow over(C)}_(o) approaches (Y,Y,Y) as a approaches 0. Therefore, the saturationadjusted RGB color sample vector {right arrow over (C)}_(o) becomes agray value whose gradation level is Y. Note that the saturation adjustedRGB color sample vector {right arrow over (C)}_(o) in equation (6b) isequivalent to that in equation (2b) when α≧1.

FIG. 6 shows a block diagram of a circuit 40 for performing this exampleof the second embodiment of the method for color saturation adjustment.The white and color tone separator 42 decomposes the input color vector{right arrow over (C)}=(R,G,B) into a white vector {right arrow over(w)} and a color tone vector {right arrow over(C)}_(T)=(R_(T),G_(T),B_(T)) as described by equation (1). Thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))} isobtained using the multiplier 44, which performs the operation {rightarrow over (C)}_(T) ^(o)=α·{right arrow over (C)}_(T). The minimum valueselection circuit 46 obtains the minimum value selected from one and thecolor saturation adjusting gain α, and provides the result as the graymixing ratio α_(g). The output signal of the mixer 48 is {right arrowover (Y)}·(1−α_(g))+{right arrow over (w)}·α_(g). The saturationadjusted RGB color sample vector {right arrow over (C)}_(o) is obtainedfrom the adder 50, which adds the saturation adjusted color tone vector{right arrow over (C_(T) ^(o))} and the term {right arrow over(Y)}·(1−α_(g))+{right arrow over (w)}·α_(g) obtained from the mixer 48.

FIG. 7 shows a block diagram of a particular implementation of thecircuit 50 for performing the second embodiment of the method for colorsaturation adjustment. The circuit 50 implements equation (3) to performthe decomposition. The white vector calculation circuit 52 calculates aluminance value Y from the RGB color sample vector {right arrow over(C)} and constructs a white vector {right arrow over (w)}. Eachcomponent of the white vector {right arrow over (w)} is equal to theluminance value Y. The vector summer 54 subtracts the white vector{right arrow over (w)} from the RGB color sample vector {right arrowover (C)} to obtain the color tone vector {right arrow over (C_(T))}.The multiplier 56 multiplies the color tone vector {right arrow over(C_(T))} by the color saturation adjusting gain α to obtain thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))}.The minimum value selection circuit 58 chooses a minimum value from oneand the color saturation adjusting gain α, and provides the result asthe gray mixing ratio α_(g). The output signal of the mixer 60 is {rightarrow over (Y)}·(1−α_(g))+{right arrow over (w)}·α_(g). The saturationadjusted RGB color sample vector {right arrow over (C)}_(o) is obtainedfrom the adder 62, which adds the saturation adjusted color tone vector{right arrow over (C_(T) ^(o))} and the term {right arrow over(Y)}·(1−α_(g))+{right arrow over (w)}·α_(g) that is obtained from themixer 60.

One common drawback of the first and second embodiments of the methodfor color saturation adjustment is that a color can be saturated. Thatis, depending on the degree of the color saturation level of the inputsample and the requested value of the color saturation adjusting gain α,the resulting saturation adjusted RGB color vector {right arrow over(C)}_(o)=(R_(o),G_(o),B_(o)) can be mapped to outside the color gamut ofthe R,G,B signals (i.e., R>255, G>255, and/or B>255). In other words,the saturation adjusted RGB color vector {right arrow over (C)}_(T)^(o)=α·{right arrow over (C_(T))} can be saturated depending on thesaturation level of {right arrow over (C_(T))} and α. Hence, anoptionally provided feature of the invention is the development of colorsaturation limiting functions that can be incorporated into the methodfor color saturation adjustment in an RGB color system.

We will calculate the magnitude of the color tone vector {right arrowover (C_(T))} and associate this magnitude with the saturation level ofthe color tone vector {right arrow over (C_(T))}. Remember that thecolor tone vector {right arrow over (C_(T))} has the components(R_(T),G_(T),B_(T)). We can calculate the magnitude, which we haveassociated with the saturation level of the color tone vector {rightarrow over (C_(T))}, using the following equation:S({right arrow over (C _(T))})=√{square root over (R _(T) ² +G _(T) ² +B_(T) ²)}.  (7)We can alternatively approximate the saturation level using thefollowing equation:S({right arrow over (C)} _(T))=|R _(T) |+|G _(T) |+|B _(T)|.  (8a)Depending upon the application, various different forms of calculatingthe saturation level can be defined and the invention should not belimited to any one particular way of calculating this saturation level.For example, some additional ways of calculating the saturation levelinclude:

$\begin{matrix}{{{S\left( \overset{\rightarrow}{C_{T}} \right)} = {\max\left( {R_{T}^{2},G_{T}^{2},B_{T}^{2}} \right)}};} & \left( {8b} \right) \\{{{S\left( \overset{\rightarrow}{C_{T}} \right)} = {\max\left( {{R_{T}},{G_{T}},{B_{T}}} \right)}};} & \left( {8c} \right) \\{{{{{S\left( \overset{\rightarrow}{C_{T}} \right)} = \sqrt{\left( {R_{T}^{2} + G_{T}^{2} + B_{T}^{2}} \right) + \left( {R_{T} - G_{T}} \right)^{2} + \left( {G_{T} - B_{T}} \right)^{2} + \left( {B_{T} - R_{T}} \right)^{2}}};}{and}}\;} & \left( {8d} \right) \\{{S\left( \overset{\rightarrow}{C_{T}} \right)} = {{R_{T}} + {G_{T}} + {B_{T}} + {{R_{T} - G_{T}}} + {{G_{T} - B_{T}}} + {{{B_{T} - R_{T}}}.}}} & \left( {8e} \right)\end{matrix}$

Thus far, we have disclosed, two embodiments of the method for colorsaturation adjustment. Examples have been given in equations (3)-(5) ofhow to decompose the digital RGB color input sample vector {right arrowover (C)}=(R,G,B) into a white vector {right arrow over (w)} and a colortone vector C_(T), however, the invention should not be construed asbeing limited to these examples of the decomposition. Examples have beengiven in equations (7) and (8a)-(8e) of how to calculate the saturationlevel of the color tone vector {right arrow over (C_(T))}, however, asalready discussed, the invention should not be construed as beinglimited to these examples of calculating the saturation level.

In the following text, four embodiments of a method for calculating thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))}will be disclosed. These embodiments of the method for calculating thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))}use different forms of the saturation adjustment parameter P. Any one ofthese embodiments for calculating the saturation adjusted color tonevector {right arrow over (C_(T) ^(o))} can be used together with thefirst and second embodiments of the method for color saturationadjustment.

The first embodiment of the method of calculating the saturationadjusted color tone vector {right arrow over (C_(T) ^(o))} includesdeveloping a saturation limiting parameter β that will be multipliedtogether with α·{right arrow over (C_(T))} in order to limit thesaturation level to a certain level. That is, the saturation adjustedcolor tone vector {right arrow over (C_(T) ^(o))} is given as:{right arrow over (C)} _(T) ^(o) =β·α·{right arrow over (C)} _(T).  (9)FIG. 8 shows two multipliers 60 and 62 connected to perform theoperation described in equation (9). Accordingly, when using the firstembodiment of the method for calculating the saturation adjusted colortone vector {right arrow over (C_(T) ^(o))} in conjunction with thefirst embodiment of the method for color saturation adjustment asexpressed in equation (2a), we define the saturation adjustmentparameter P as being β·α. Similarly, when using the first embodiment ofthe method for calculating the saturation adjusted color tone vector{right arrow over (C_(T) ^(o))} in conjunction with the secondembodiment of the method for color saturation adjustment as expressed inequation (6a), we define the saturation adjustment parameter P as beingβ·α.

Now the question is how to formulate the saturation limiting parameterβ. Note that the purpose of multiplying the saturation limitingparameter β with α·{right arrow over (C_(T))} as expressed in equation(9) is to prevent the saturation level of α·{right arrow over (C_(T))}from exceeding a certain saturation level.

If the saturation level S(α·{right arrow over (C)}_(T)) is less than acertain level, which implies that α·{right arrow over (C_(T))} is “notsaturated”, then it is obvious from the purpose of introducing thesaturation limiting parameter β that β should be equal to one. Hence, itcan be stated that:β=1 if S(α·{right arrow over (C)} _(T))≦L,  (10)where L denotes a pre-determined saturation level to which we want tolimit the color saturation level of the adjusted color samples.Hereinafter, L will be referred to as a predetermined limit value. Itcan be stated that:{right arrow over (C)} _(T) ^(o) =α·{right arrow over (C)} _(T),  (11)when S(α·{right arrow over (C)}_(T))≦L.

Now in the case when S(α·{right arrow over (C)}_(T))>L, we need tomultiply α·{right arrow over (C)}_(T) and the saturation limitingparameter β together so that the color saturation level of the resultingsaturation adjusted color tone vector {right arrow over (C)}_(T) ^(o)can be adjusted as a factor of β in order to prevent a possiblesaturation. The following constraint is imposed:S({right arrow over (C)} _(T) ^(o))=L.From the definition given in (7) or (8a), for example, it is noted that:S({right arrow over (C)} _(T) ^(o))=S(β·α{right arrow over (C)}_(T))=β·S(α·{right arrow over (C)} _(T)).We then obtain the following saturation limiting parameter:

$\begin{matrix}{\beta = {\frac{L}{S\left( {\alpha \cdot {\overset{\rightarrow}{C}}_{T}} \right)}.}} & (12)\end{matrix}$

In summary, the saturation adjustment parameter P is chosen to be thecolor saturation adjusting gain α multiplied by the saturation limitingparameter β. The saturation adjusted color tone vector {right arrow over(C_(T) ^(o))} is then calculated according to the following equation:

$\begin{matrix}{{{\overset{\rightarrow}{C}}_{T}^{o} = {\beta \cdot \alpha \cdot {\overset{\rightarrow}{C}}_{T}}},{where}} & (13) \\{\beta = \left\{ \begin{matrix}1 & {if} & {{S\left( {\alpha \cdot {\overset{\rightarrow}{C}}_{T}} \right)} \leq L} \\\frac{L}{S\left( {\alpha \cdot {\overset{\rightarrow}{C}}_{T}} \right)} & {else} & \;\end{matrix} \right.} & (14)\end{matrix}$

FIG. 9 shows a block diagram of a circuit 70 for performing the firstembodiment of the method of calculating the saturation adjusted colortone vector {right arrow over (C_(T) ^(o))}. The multiplier 72multiplies the color tone vector {right arrow over (C_(T))} by the colorsaturation adjusting gain α. The saturation calculation circuit 74calculates the saturation level S(α·{right arrow over (C)}_(T)) and theβ-selection circuit 76 chooses the value of the saturation limitingparameter β in accordance with equation (14). The saturation adjustedcolor tone vector {right arrow over (C_(T) ^(o))} is obtained from themultiplier 78, which multiplies β and α·{right arrow over (C)}_(T).

A second embodiment of the method for calculating the saturationadjusted color tone vector {right arrow over (C_(T) ^(o))} will now bedeveloped. If we note that S(α·{right arrow over (C)}_(T))=α·S({rightarrow over (C)}_(T)) and combine it with equations (13) and (14), weobtain:

$\begin{matrix}{{{\overset{\rightarrow}{C}}_{T}^{o} = {r \cdot {\overset{\rightarrow}{C}}_{T}}}{{where}:}} & (15) \\{r = \left\{ \begin{matrix}\alpha & {if} & {{S\left( {\overset{\rightarrow}{C}}_{T} \right)} \leq \frac{L}{\alpha}} \\\frac{L}{S\left( {\overset{\rightarrow}{C}}_{T} \right)} & {else} & \;\end{matrix} \right.} & (16)\end{matrix}$The result obtained when using equations (15) and (16) to calculate thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))} isequivalent to the result obtained when using equations (13) and (14).Note, however, when equations (15) and (16) are used to calculate thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))},less computation is required than when using equations (13) and (14).Accordingly, when using the second embodiment of the method forcalculating the saturation adjusted color tone vector {right arrow over(C_(T) ^(o))} in conjunction with the first embodiment of the method forcolor saturation adjustment as expressed in equation (2a), or the secondembodiment of the method for color saturation adjustment as expressed inequation (6a), we define the saturation adjustment parameter P as beingr.

FIG. 10 shows a block diagram of a circuit 80 for performing the secondmethod of calculating the saturation adjusted color tone vector {rightarrow over (C_(T) ^(o))}. The saturation calculation circuit 82calculates the saturation level S({right arrow over (C)}_(T)) and ther-selection circuit 84 chooses the value of r in accordance withequation (16). The saturation adjusted color tone vector {right arrowover (C_(T) ^(o))} is obtained from the multiplier 86, which multipliesr and {right arrow over (C)}_(T).

A third embodiment of the method for calculating the saturation adjustedcolor tone vector {right arrow over (C_(T) ^(o))} will now be developed.The saturation adjusted color tone vector {right arrow over (C_(T)^(o))} can be expressed according to the following equation:{right arrow over (C)} _(T) ^(o) =x·{right arrow over (C)} _(T),  (17)where x denotes a real color adjusting gain defined by:

$\begin{matrix}{x = \left\{ \begin{matrix}\alpha & {if} & {0 \leq \alpha \leq 1} \\{f\left( {S\left( {\overset{\rightarrow}{C}}_{T} \right)} \right)} & {if} & {\alpha > 1}\end{matrix} \right.} & (18)\end{matrix}$The mathematical function ƒ(S({right arrow over (C)}_(T))) can be anyfunction that satisfies the following conditions:

-   -   ƒ(S({right arrow over (C)}_(T))) is a monotonically decreasing        function with respect to S({right arrow over (C)}_(T)) for        0≦S({right arrow over (C)}_(T))≦L where L is a predetermined        constant limit value;    -   ƒ(0)=α; and    -   ƒ(S({right arrow over (C)}_(T)))=1 for S({right arrow over        (C)}_(T))≧L.        Note that the last condition ensures no change is made in the        color saturation level of the input sample when its color        saturation level exceeds a certain level even though the color        saturation adjusting gain is large (α>1). Examples of ƒ(S({right        arrow over (C)}_(T))) are shown in FIGS. 11, 12, and 13. For        instance, in FIG. 11, x=ƒ(S({right arrow over (C)}_(T))) for        0≦S({right arrow over (C)}_(T))≦L can be expressed as:

$x = {1 + {\left( {\alpha - 1} \right) \cdot {\frac{\left( {L - {S\left( {\overset{\rightarrow}{C}}_{T} \right)}} \right) \cdot \left( {L + {S\left( {\overset{\rightarrow}{C}}_{T} \right)}} \right)}{L^{2}}.}}}$Because of the constraints on ƒ(S({right arrow over (C)}_(T))), whenS({right arrow over (C)}_(T))≧L, the real color adjusting gain xbecomes:

$x = \left\{ \begin{matrix}\alpha & {if} & {0 \leq \alpha \leq 1} \\1 & {if} & {\alpha > 1}\end{matrix} \right.$When using the third embodiment of the method for calculating thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))} inconjunction with the first embodiment of the method for color saturationadjustment as expressed in equation (2a) or with the second embodimentof the method for color saturation adjustment as expressed in equation(6a), we define the saturation adjustment parameter P as being the realcolor adjusting gain x.

FIG. 14 shows a block diagram of a circuit 90 for performing the thirdembodiment of the method for calculating the saturation adjusted colortone vector {right arrow over (C_(T) ^(o))}. The saturation calculationcircuit 92 calculates the saturation level S({right arrow over(C)}_(T)). The circuit 94 for calculating ƒ(S({right arrow over(C)}_(T))) evaluates ƒ(S({right arrow over (C)}_(T))) at the saturationlevel S({right arrow over (C)}_(T)). The real color adjusting gaincircuit 96 chooses the value of x in accordance with equation (18). Thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))} isobtained from the multiplier 98, which multiplies x and {right arrowover (C)}_(T).

A fourth embodiment of the method for calculating the saturationadjusted color tone vector {right arrow over (C_(T) ^(o))} will now bedeveloped. We will limit the saturation level of the saturation adjustedcolor tone vector {right arrow over (C)}_(T) ^(o)=x·{right arrow over(C)}_(T) such that:S({right arrow over (C)} _(T) ^(o))=x·S({right arrow over (C)} _(T))≦L.When S({right arrow over (C)}_(T))≦L and α>1, the following condition isobtained:

$\begin{matrix}{x \leq \frac{L}{S\left( {\overset{\rightarrow}{C}}_{T} \right)}} & (19)\end{matrix}$By combining equations (18) and (19), we obtain the followingrelationship for the real color adjusting gain:

$\begin{matrix}{x = \left\{ {\begin{matrix}\alpha & {{{if}\mspace{14mu} 0} \leq \alpha \leq 1} \\{\min\left( {{f\left( {S\left( {\overset{\rightarrow}{C}}_{T} \right)} \right)},\frac{L}{S\left( {\overset{\rightharpoonup}{C}}_{T} \right)}} \right)} & {{{if}\mspace{14mu}\alpha} > {1\mspace{14mu}{and}\mspace{14mu}{S\left( {\overset{\rightarrow}{C}}_{T} \right)}} \leq L} \\1 & {{{if}\mspace{14mu}\alpha} > {1\mspace{14mu}{and}\mspace{14mu}{S\left( {\overset{\rightarrow}{C}}_{T} \right)}} > L}\end{matrix}.} \right.} & (20)\end{matrix}$When using the fourth embodiment of the method for calculating thesaturation adjusted color tone vector {right arrow over (C_(T) ^(o))} inconjunction with the first embodiment of the method for color saturationadjustment as expressed in equation (2a) or with the second embodimentof the method for color saturation adjustment as expressed in equation(6a), we define the saturation adjustment parameter P as being the realcolor adjusting gain x.

FIG. 15 is a flowchart illustrating the steps used to implement thefourth embodiment of the method for calculating the saturation adjustedcolor tone vector {right arrow over (C_(T) ^(o))} in accordance withequations (17) and (20). In step 1, the color saturation adjusting gainα and the color tone vector {right arrow over (C_(T))} are acquired. Instep 2, it is determined whether the color saturation adjusting gain αis equal to or less than 1. If so, the real color adjusting gain x isset equal to α in step 9. If the color saturation adjusting gain α isnot equal to or less than 1, then in step 3, the saturation level of thecolor tone vector {right arrow over (C_(T))} is determined. In step 4,it is determined whether the saturation level of the color tone vector{right arrow over (C_(T))} is greater than the predetermined limit L. Ifthe saturation level of the color tone vector {right arrow over (C_(T))}is greater than the predetermined limit L, then in step 5, the realcolor adjusting gain x is set equal to 1. If the saturation level of thecolor tone vector {right arrow over (C_(T))} is not greater than thepredetermined limit L, then in step 6, a first value is obtained byevaluating the mathematical function ƒ at the value of the saturationlevel of the color tone vector {right arrow over (C_(T))}, and a secondvalue is obtained by dividing the predetermined limit L by thesaturation level of the color tone vector {right arrow over (C_(T))}.Additionally in step 6, a minimum value is selected from the first valueand the second value and the real color adjusting gain x is set equal tothis minimum value. As can be seen in FIG. 15, step 7 can follow eitherstep 9, 5, or 6. In step 7, a saturation adjusted color tone vector{right arrow over (C_(T) ^(o))} is obtained by multiplying the realcolor adjusting gain x with the color tone vector {right arrow over(C_(T))}. The saturation adjusted color tone vector {right arrow over(C_(T) ^(o))} can then be used in equation (2a) to perform the firstembodiment of the method for color saturation adjustment, or in equation(6a) to perform the second embodiment. Step 8 causes the procedure toloop back to step 1 to obtain the next color tone vector {right arrowover (C_(T))}, which may represent another pixel of the same inputimage, or which may possibly represent the first pixel of a subsequentinput image.

A circuit for performing the fourth embodiment of the method forcalculating the saturation adjusted color tone vector {right arrow over(C_(T) ^(o))} can be constructed similarly to the circuit 90 shown inFIG. 14. The difference will be that the real color adjusting gaincircuit 96 will choose the value of x in accordance with equation (20).

1. A method for adjusting a color saturation level of at least one colorpixel of an input image obtained from a time varying RGB video signal,comprising: employing an RGB color processor for decomposing an RGBcolor sample representing the at least one color pixel into color toneinformation including a color tone vector having a directionrepresentative of the hue of the color sample and a magnituderepresentative of the saturation of the color sample; determining asaturation adjusted color tone based on the color tone vector and asaturation adjustment parameter; and determining a saturation adjustedRGB color sample based on the saturation adjusted color tone.
 2. Themethod of claim 1, wherein: the steps of decomposing an RGB color samplefurther includes the steps of: obtaining an RGB color sample vector{right arrow over (C)} representing the color pixel of the input imageobtained from the time varying RGB video signal; decomposing the RGBcolor sample vector {right arrow over (C)} into a white vector {rightarrow over (w)} and a color tone vector {right arrow over (C)}_(T); thesteps of determining a saturation adjusted color tone further includesthe steps of obtaining a saturation adjusted color tone vector {rightarrow over (C_(T) ^(O))} by multiplying the color tone vector {rightarrow over (C)}_(T) by a saturation adjustment parameter; the steps ofdetermining a saturation adjusted RGB color sample further includes thesteps of obtaining a saturation adjusted RGB color sample vector {rightarrow over (C)}_(o) by adding the white vector {right arrow over (w)}and the saturation adjusted color tone vector {right arrow over (C_(T)^(O))}; and the method further comprising the step of using thesaturation adjusted RGB color sample vector {right arrow over (C)}_(o)to represent a color pixel of an output image.
 3. The method accordingto claim 2, which comprises: defining a luminance vector {right arrowover (Y)} where each component of the luminance vector {right arrow over(Y)} is a luminance value obtained from the RGB color sample vector{right arrow over (C)}; configuring the saturation adjustment parameterto include at least a color saturation adjusting gain α; obtaining agray mixing ratio α_(g) by selecting a minimum value from the groupconsisting of one and the color saturation adjusting gain α; obtaining agray level adjusted vector by multiplying the luminance vector {rightarrow over (Y)} by a quantity obtained by subtracting the gray mixingratio α_(g) from one; and performing the step of obtaining thesaturation adjusted RGB color sample vector {right arrow over (C)}_(o)by: before adding the white vector {right arrow over (w)} and thesaturation adjusted color tone vector {right arrow over (C_(T) ^(O))},multiplying the white vector {right arrow over (w)} by the gray mixingratio α_(g), and when adding the white vector {right arrow over (w)},which has been multiplied by the gray mixing ratio α_(g), and thesaturation adjusted color tone vector {right arrow over (C_(T) ^(O))},also adding thereto, the gray level adjusted vector to obtain thesaturation adjusted RGB color sample vector {right arrow over (C)}_(o).4. The method according to claim 2, which comprises: acquiring asaturation adjusting gain α; and using the saturation adjusting gain αas the saturation adjustment parameter.
 5. The method according to claim2, which comprises: acquiring a saturation adjusting gain α; determininga saturation level S(α·{right arrow over (C)}_(T)) of a quantityobtained by multiplying the saturation adjusting gain α by the colortone vector {right arrow over (C)}_(T); and if the saturation levelS(α·{right arrow over (C)}_(T)) is greater than a predetermined limitvalue L, then: obtaining a saturation limiting parameter β by dividingthe predetermined limit value L by the saturation level S(α·{right arrowover (C)}_(T)), and obtaining the saturation adjustment parameter bymultiplying the saturation adjusting gain α by the saturation limitingparameter β.
 6. The method according to claim 5, which comprises: if thesaturation level S(α·{right arrow over (C)}_(T)) is not greater than thepredetermined limit value L, then: setting the saturation limitingparameter β equal to one, and obtaining the saturation adjustmentparameter by multiplying the saturation adjusting gain α by thesaturation limiting parameter β.
 7. The method according to claim 5,which comprises: if the saturation level S(α·{right arrow over (C)}_(T))is not greater than the predetermined limit value L, then using thesaturation adjusting gain α as the saturation adjustment parameter. 8.The method according to claim 2, which comprises: acquiring a saturationadjusting gain α; determining a saturation level S({right arrow over(C)}_(T)) of the color tone vector {right arrow over (C)}_(T); if thesaturation level S({right arrow over (C)}_(T)) of the color tone vector{right arrow over (C)}_(T) is not greater than a predetermined limitvalue L divided by the saturation adjusting gain α, then using thesaturation adjusting gain α as the saturation adjustment parameter; andif the saturation level S({right arrow over (C)}_(T)) is greater thanthe predetermined limit value L divided by the saturation adjusting gainα, then setting the saturation adjustment parameter equal to a valueobtained by dividing the predetermined limit value L by the saturationlevel S({right arrow over (C)}_(T)) of the color tone vector {rightarrow over (C)}_(T).
 9. The method according to claim 2, whichcomprises: acquiring a saturation adjusting gain α; and if thesaturation adjusting gain α is not less than zero and not greater thanone, then using the saturation adjusting gain α as the saturationadjustment parameter that is multiplied by the color tone {right arrowover (C)}_(T) to thereby set a saturation level of the saturationadjusted color tone vector {right arrow over (C_(T) ^(O))}.
 10. Themethod according to claim 9, which comprises: selecting a mathematicalfunction that is a monotonically decreasing function with respect to anargument as the argument varies between zero and a predetermined limitvalue L; ensuring that when the mathematical function is evaluated usingan argument that equals zero, the mathematical function equals thesaturation adjusting gain α; ensuring that when the mathematicalfunction is evaluated at values of the argument being not less than thepredetermined limit value L, the mathematical function equals one; andif the saturation adjusting gain α is greater than one, then:determining a saturation level S({right arrow over (C)}_(T)) of thecolor tone vector {right arrow over (C)}_(T), using the saturation levelS({right arrow over (C)}_(T)) of the color tone vector {right arrow over(C)}_(T) as the argument and evaluating the mathematical function toobtain a value of the mathematical function, and using the value of themathematical function as the saturation adjustment parameter that ismultiplied by the color tone vector {right arrow over (C)}_(T) tothereby set the saturation level of the saturation adjusted color tonevector {right arrow over (C_(T) ^(O))}.
 11. The method according toclaim 9, which comprises: determining a saturation level S({right arrowover (C)}_(T)) of the color tone vector {right arrow over (C)}_(T); andif the saturation level S({right arrow over (C)}_(T)) of the color tonevector {right arrow over (C)}_(T) is not less than a predetermined limitL and if the saturation adjusting gain α is greater than one, then:setting the saturation adjustment parameter that is multiplied by thecolor tone vector {right arrow over (C)}_(T) to a value of one tothereby set the saturation level of the saturation adjusted color tonevector {right arrow over (C_(T) ^(O))}.
 12. The method according toclaim 9, which comprises: selecting a mathematical function that is amonotonically decreasing function with respect to an argument as theargument varies between zero and a predetermined limit value L; ensuringthat when the mathematical function is evaluated using an argument thatequals zero, the mathematical function equals the saturation adjustinggain α; ensuring that when the mathematical function is evaluated atvalues of the argument being not less than the predetermined limit valueL, the mathematical function equals one; determining a saturation levelS({right arrow over (C)}_(T)) of the color tone vector {right arrow over(C)}_(T); if the saturation level S({right arrow over (C)}_(T)) of thecolor tone vector {right arrow over (C)}_(T) is not greater than thepredetermined limit value L and if the saturation adjusting gain α isgreater than one, then: using the saturation level S({right arrow over(C)}_(T)) of the color tone vector {right arrow over (C)}_(T) as theargument and evaluating the mathematical function to obtain a value ofthe mathematical function, selecting a minimum value from the groupconsisting of the value of the mathematical function, evaluated usingthe saturation level S({right arrow over (C)}_(T)) of the color tonevector {right arrow over (C)}_(T), and a value obtained from dividingthe predetermined limit value L by the saturation level S({right arrowover (C)}_(T)) of the color tone vector {right arrow over (C)}_(T), andsetting the saturation adjustment parameter that is multiplied by thecolor tone vector {right arrow over (C)}_(T) to be equal to the minimumvalue such that the saturation level of the saturation adjusted colortone vector {right arrow over (C_(T) ^(O))} is thereby set; and if thesaturation level S({right arrow over (C)}_(T)) of the color tone vector{right arrow over (C)}C_(T) is greater than the predetermined limitvalue L and if the saturation adjusting gain α is greater than one,then: setting the saturation adjustment parameter that is multiplied bythe color tone vector {right arrow over (C)}_(T) to be equal to one tothereby set the saturation level of the saturation adjusted color tonevector {right arrow over (C_(T) ^(O))}.
 13. A method for adjusting acolor saturation level of at least one color pixel of an input imageobtained from a time varying RGB video signal, comprising: employing anRGB color processor for decomposing an RGB color sample representing theat least one color pixel into color tone information including a colortone vector having a direction representative of the hue of the colorsample and a magnitude representative of the saturation of the colorsample; determining a saturation adjusted color tone based on the colortone vector and a saturation adjustment parameter; and determining asaturation adjusted RGB color sample based on the saturation adjustedcolor tone; wherein: the step of decomposing an RGB color sample furtherincludes the steps of: obtaining an RGB color sample vector {right arrowover (C)} representing the color pixel of the input image obtained fromthe time varying RGB video signal; decomposing the RGB color samplevector {right arrow over (C)} into a white vector {right arrow over (w)}and a color tone vector {right arrow over (C)}_(T); the step ofdetermining a saturation adjusted color tone further includes the stepsof: obtaining a saturation adjusted color tone vector {right arrow over(C_(T) ^(O))} by multiplying the color tone vector {right arrow over(C)}_(T) by the saturation adjustment parameter; the steps ofdetermining a saturation adjusted RGB color sample further includes thestep of: obtaining a saturation adjusted RGB color sample vector {rightarrow over (C)}_(o) by adding the white vector {right arrow over (w)}and the saturation adjusted color tone vector {right arrow over (C_(T)^(O))}; and the method further comprising the steps of: using thesaturation adjusted RGB color sample vector {right arrow over (C)}_(o)to represent a color pixel of an output image; and before performing thestep of obtaining the saturation adjusted color tone vector {right arrowover (C_(T) ^(O))}, determining a saturation level S({right arrow over(C)}_(T)) of the color tone vector {right arrow over (C)}_(T), andchoosing a value of the saturation adjustment parameter in dependence onthe saturation level S({right arrow over (C)}_(T)) of the color tonevector {right arrow over (C)}_(T) by estimating a magnitude of the colortone vector {right arrow over (C)}_(T).
 14. The method according toclaim 13, which comprises: representing the color tone vector {rightarrow over (C)}_(T) with components (R_(T), G_(T), B_(T)); anddetermining the saturation level S({right arrow over (C)}_(T)) of thecolor tone vector {right arrow over (C)}_(T) using formula:S({right arrow over (C)}_(T))=√{square root over (R _(T) ² +G _(T) ² +B_(T) ²)}.
 15. The method according to claim 13, which comprises:representing the color tone vector {right arrow over (C)}_(T) withcomponents (R_(T), G_(T), B_(T)); and determining the saturation levelS({right arrow over (C)}_(T)) of the color tone vector {right arrow over(C)}_(T) using formula:S({right arrow over (C)} _(T))=|R _(T) |+|G _(T) |+|B _(T)|.
 16. Themethod according to claim 13, which comprises: representing the colortone vector {right arrow over (C)}_(T) with components (R_(T), G_(T),B_(T)); and determining the saturation level S({right arrow over(C)}_(T)) of the color tone vector {right arrow over (C)}_(T) usingformula:S({right arrow over (C)} _(T))=max(R _(T) ² , G _(T) ² , B _(T) ²). 17.The method according to claim 13, which comprises: representing thecolor tone vector {right arrow over (C)}_(T) with components (R_(T),G_(T), B_(T)); and determining the saturation level S({right arrow over(C)}_(T)) of the color tone vector {right arrow over (C)}_(T) usingformula:S({right arrow over (C)}_(T))=max(|R _(T) |,|G _(T) |,|B _(T)|).
 18. Themethod according to claim 13, which comprises: representing the colortone vector {right arrow over (C)}_(T) with components (R_(T), G_(T),B_(T)); and determining the saturation level S({right arrow over(C)}_(T)) of the color tone vector {right arrow over (C)}_(T) usingformula:${S\left( {\overset{\rightarrow}{C}}_{T} \right)} = {\sqrt{\left( {R_{T}^{2} + G_{T}^{2} + B_{T}^{2}} \right) + \left( {R_{T} - G_{T}} \right)^{2} + \left( {G_{T} - B_{T}} \right)^{2} + \left( {B_{T} - R_{T}} \right)^{2}}.}$19. The method according to claim 13, which comprises: representing thecolor tone vector {right arrow over (C)}_(T) with components (R_(T),G_(T), B_(T)); and determining the saturation level S({right arrow over(C)}_(T)) of the color tone vector {right arrow over (C)}_(T) usingformula:S({right arrow over (C)}_(T))=|R _(T) |+|G _(T) |+|B _(T) |+|R _(T) −G_(T) |+|G _(T) −B _(T) |+|B _(T) −R _(T)|.
 20. The method according toclaim 2, which comprises: performing the step of decomposing the RGBcolor sample vector {right arrow over (C)}_(T) by: representing the RGBcolor sample vector {right arrow over (C)}_(T) with components (R, G,B); calculating a luminance value Y from the RGB color sample vector{right arrow over (C)}, determining the white vector {right arrow over(w)} according to equation: {right arrow over (w)}=(Y, Y, Y), anddetermining the color tone vector {right arrow over (C)}_(T) accordingto equation:{right arrow over (C)} _(T)=(R−Y,G−Y,B−Y).
 21. The method according toclaim 2, which comprises: performing the step of decomposing the RGBcolor sample vector {right arrow over (C)} by: representing the RGBcolor sample vector {right arrow over (C)} with components (R, G, B);determining the white vector {right arrow over (w)} according toequation:${\overset{\rightarrow}{w} = \left( {X,X,X} \right)},{{{where}\mspace{14mu} X} = \frac{R + G + B}{3}},$and determining the color tone vector {right arrow over (C)}_(T)according to equation:{right arrow over (C)} _(T)=(R−X,G−X,B−X).
 22. The method according toclaim 2, which comprises: performing the step of decomposing the RGBcolor sample vector {right arrow over (C)} by: representing the RGBcolor sample vector {right arrow over (C)} with components (R, G, B);determining the white vector {right arrow over (w)} according toequation:${\overset{\rightarrow}{w} = \left( {X,X,X} \right)},{{{where}\mspace{14mu}\overset{\rightarrow}{w}} = \frac{G + B}{2}},\frac{R + B}{2},\frac{R + G}{2},$and determining the color tone vector {right arrow over (C)}_(T)according to equation:${\overset{\rightarrow}{C}}_{T} = \left( {{R - \frac{G + B}{2}},{G - \frac{R + B}{2}},{B - {\frac{R + G}{2}.}}} \right.$23. The method according to claim 2, which comprises: defining aluminance vector {right arrow over (Y)} where each component of theluminance vector {right arrow over (Y)} is a luminance value obtainedfrom the RGB color sample vector {right arrow over (C)}; acquiring acolor saturation adjusting gain α; obtaining a gray mixing ratio α_(g)by selecting a minimum value from the group consisting of one and thecolor saturation adjusting gain α; obtaining a gray level adjustedvector by multiplying the luminance vector {right arrow over (Y)} by aquantity obtained by subtracting the gray mixing ratio α_(g) from one;and performing the step of obtaining the saturation adjusted RGB colorsample vector {right arrow over (C)}_(o) by: before adding the whitevector {right arrow over (w)} and the saturation adjusted color tonevector {right arrow over (C_(T) ^(O))}, multiplying the white vector{right arrow over (w)} by the gray mixing ratio α_(g), and when addingthe white vector {right arrow over (w)}, which has been multiplied bythe gray mixing ratio α_(g), and the saturation adjusted color tonevector {right arrow over (C_(T) ^(O))}, also adding thereto, the graylevel adjusted vector to obtain the saturation adjusted RGB color samplevector {right arrow over (C)}_(o).